The disclosed technology relates to additives that impart basicity (measured as TBN) to a lubricant formulation without adding metal (measured as Sulfated Ash). The additives do not lead to deterioration of elastomer seals.
It is known that lubricants become less effective during their use due to exposure to the operating conditions of the device they are used in, and particularly due to exposure to by-products generated by the operation of the device. For example, engine oil becomes less effective during its use, in part due to exposure of the oil to acidic and pro-oxidant byproducts. These byproducts result from the incomplete combustion of fuel in devices such as internal combustion engines, which utilize the oil. These byproducts lead to deleterious effects in the engine oil and likewise in the engine. The byproducts may, for example, oxidize hydrocarbons found in the lubricating oil, yielding carboxylic acids and other oxygenates. These oxidized and acidic hydrocarbons can then go on to cause corrosion, wear and deposit problems.
Base-containing additives are added to lubricants in order to neutralize such byproducts, thus reducing the harm they cause to the lubricant and to the device. Over-based calcium or magnesium carbonate detergents have been used for some time as acid scavengers, neutralizing these byproducts and so protecting both the lubricant and the device. However, over-based detergents carry with them an abundance of metal as measured by sulfated ash. New industry upgrades for diesel and passenger car lubricating oils are putting ever decreasing limits on the amount of sulfated ash, and by extension the amount of over-based detergent, permissible in an oil. Therefore, a source of base that consists of only N, C, H, and O atoms is extremely desirable.
There are two common measures of basicity that are used in the field of lubricant additives. Total Base Number (TBN) may be as measured by ASTM D 2896, which is a titration that measures both strong and weak bases. On the other hand, ASTM D 4739 is a titration that measures strong bases but does not readily titrate weak bases such as certain amines, including many aromatic amines. Many lubricant applications desire TBN as measured by ASTM D 4739, making many amities less than satisfactory sources of basicity.
Basic amine additives have nevertheless been investigated as alternatives to ash containing over-based metal detergents, for example, alkyl and aromatic amines. However, the addition of basic amine additives can lead to additional detrimental effects. For example, it is known that alkyl and some aromatic amines tend to degrade fluoroelastomeric seals materials. These basic amine additives, such as succinimide dispersants, contain polyamine groups, which provide a source of basicity. However, such amines are believed to cause dehydrofluorination in fluoroelastomeric seals materials, such as Viton® seals, which is believed to be a first step in seals degradation. Seal degradation may lead to seal failure, such as seal leaks, harming engine performance and possibly causing engine damage. Generally, the base content, or total base number (TBN), of a lubricant can only be boosted modestly by such a basic amine before seals degradation becomes a significant issue, limiting the amount of TBN that can be provided by such additives.
U.S. Patent Publication 2012-0040876, Preston et al., Feb. 16, 2012, discloses anthranilic esters as additives in lubricants. This document discloses compositions that are said to deliver an ash-free base to a lubricant in the form of a basic amine additive, without adversely impacting seal compatibility. The examples report TBN values of 150-188 as measured by D2896. (D 2896 measurement captures the basicity of weak bases as well as strong bases.)
The disclosed technology, therefore, solves the problem of providing strong basicity, as measured by ASTM D 4739, to a lubricant, without imparting additional metal content (sulfated ash) thereto and while not leading to deterioration of elastomeric seals such as fluorocarbon seals, as measured by the Mercedes Benz supply specification MB DBL6674_FKM. This is accomplished by employing an N-hydrocarbyl-substituted δ-aminoester or δ-aminothioester as more fully described herein. As otherwise expressed, the technology provides the ability to impart relatively high TBN levels to a lubricant while maintaining the low sulfated ash levels specified by increasingly stringent governmental regulations, while at the same time protecting seal performance and compatibility.